The invention discloses a graph-merged detection and decoding algorithm of BP (Belief Proportion) based MIMO detection and polar code decoding and a device to further improve the stability of a communication system and reduce the error rate. As a factor graph of MIMO BP detection and a factor graph of polar code decoding are combined in the algorithm, the probability information between the factor graphs can be exchanged, and a more accurate log-likelihood ratio and a faster rate of convergence further can be obtained.